Depends on a lot of things.
- How many resources can you manage on your own: I don't want my work to become a project and people management job, so I will keep the team small till it starts impact work delivery and quality.
But after a certain number, 5 for me, I need either higher quality hires (more expensive) who can self manage, initiative taking - or I hire a project manager to manage these resources (again expensive). Hiring a project manager will impact culture and experience of employees which again will make me invest more in catering to these challenges.
Margins will keep moving in this process, but I look at it as managing between my own time vs margins. Either one has to suffer to gain in the other.
Over the years I have come to value my time more than margins.